Engines may use various combustion modes across different operating conditions to improve overall engine performance. Some of the different modes may require different cylinder valve operation, such as different valve timing and/or lift. For example, spark ignition (SI) combustion may be used under some conditions with a first cylinder valve operation, while controlled auto-ignition (CAI), or homogeneous charge compression ignition (HCCI), may be used under other conditions. In still another example, the cylinder may be operated without combustion, such as in a cylinder deactivation mode.
One approach to control the timing of various cylinder valve actuators to control a transition among modes (e.g., from a combustion mode to a non-combustion mode) is described in U.S. Pat. No. 5,408,966. In this example, a hydraulic actuator may be used for each cylinder of the engine to control operation of intake and exhaust valves. Specifically, the controller directs a valve to operate to begin deactivation of a selected cylinder during a predetermined intake event and the mechanism completing the deactivation by a time not later than the beginning of the next exhaust event.
The inventors herein have recognized disadvantages with such an approach. In particular, since a separate actuator is provided for each cylinder, the signal window for sending a transition signal may be limited to achieve a desired deactivation sequence between the intake and exhaust valves. And, if applying such a system to a system using cam profile switching between high and low lift profiles to enable HCCI operation, for example, such a system may have limited applicability due to the variation in timing constraints between different lift profiles (especially at high speeds, the intake valve opening time may be extremely small), and due to the limitations on the intake/exhaust valve switching order.
Thus, in one approach a method is proposed for controlling combustion modes of an engine with at least a first and second cylinder, the engine having a first actuator configured to control at least intake valves of the first and second cylinder and a second actuator configured to control at least exhaust valves of the first and second cylinder. The method comprises sending a first signal to the first actuator which adjusts operation of at least intake valves of the first and second cylinders and a second signal to the second actuator which adjusts operation of at least exhaust valves of the first and second cylinders, said first and second signals sent at different crank angles; and transitioning combustion modes of said first and second cylinders, said combustion modes including spark ignition and homogeneous compression ignition.
In this way, it is possible to take into account an engine firing order and utilize an actuator for adjusting valves of multiple cylinders. This can result in an increased window of switching valve operation. Further, it is possible to have independent control of intake and exhaust valves, for example.